I think the secret here (and this is nothing but a guess) is that the "modified potting mix" is kept really dry, is open, and that it still drains very well. Simply looking at the picture does not really tell us what the media's components are.
drdawg (Dr. Kenneth Ramsey)
The reason it's so hard to lose weight when you get up in age is because your body and your fat have become good friends.
